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Abstract
The female-sterile mutations, okra and spindle-B , cause variable axial patterning defects characteristic of defective signaling through the Gurken-Egfr pathway. A detailed characterization of the mutant phenotypes of these genes reveals that generation of the germline signal, Gurken, is affected at multiple levels. Localization of gurken mRNA is abnormal, and Gurken protein does not accumulate to wild type levels. Cloning of these two genes (in collaboration with R. Ray) has revealed that Okra and Spindle-B are homologous to yeast proteins known to function in the double strand break DNA repair pathway. To confirm the function of these genes in DNA repair, the frequency of recombination and non-disjunction was tested in the mutants. Consistent with a role for these genes in repair of the double strand breaks made during the initiation of meiotic recombination, the mutations cause a decrease in recombination frequencies and an increase in X-chromosome nondisjunction. I have determined that the production of patterning defects are a consequence of the failure to repair the double strand breaks created during the initiation of meiotic recombination—mutants which do not make these breaks suppress the okra and spindle-B mutant phenotypes. Furthermore, I found that double strand breaks do not directly impair Gurken-Egfr signaling, but rather that their presence activates a meiotic checkpoint pathway which seems to couple translation of oocyte specific proteins, such as Gurken, to progression through meiosis. Thus, mutations that bypass the checkpoint also suppress the okra and spindle-B patterning defects. Finally, I observed that the mobility of Vasa, an eIF4A-like translation factor, is altered in spindle-B mutants, suggesting that Vas is a downstream target of the meiotic checkpoint, and that modification of Vas by the checkpoint could mediate the checkpoint-dependent translational regulation of Gurken.
